Update / Insert from excel to SQL Server

My Requirement is  -
1. User will select only excel sheet in File Upload Control - Done.

2. On button click event, the user will get the worksheets of excel file in a dropdownlist (Sheet1 , Sheet2, Sheet3, Sheet4, etc)

3. Table structure -
ID Code Description Datetime (ID - PK, auto increment ; Code - unique)

4. In excel , there will be 2 columns (Code , Description).

5. System Flow - User will check if Code exists in the SQL Server table or not. If exists, then update the description. If not, then insert the Code and Description

Please guide !!